1. Field of the Invention
The present invention relates to a substrate for an ink jet recording head, particularly to a substrate for use in an ink jet recording head, which comprises a heater for generating bubbles in ink and an auxiliary heater for preheating the ink, the heaters being formed on the same base member.
2. Related Background Art
The ink jet recording system disclosed in U.S. Pat. Nos. 4,723,129 or 4,740,796 is recently attracting particular attention because it is capable of carrying out recording of high-precision and high image quality with a high speed and a high density, and is suitable for color image formation and for compaction.
In the above-mentioned ink jet recording system, the recording head in which bubbles are generated in ink by utilizing thermal energy to discharge the ink onto a recording medium, generally has a configuration in which heat-generating resistance members for generating bubbles in the ink and wirings for electrical connection are formed on the same base member to provide the substrate for the ink jet recording head and then nozzles for discharging the ink are formed thereon.
Further, recently there have been made developments to incorporate many functions into such substrate for the ink jet recording head or to increase the density thereof.
For example, Japanese Patent Application Laid-Open No. 57-72868 discloses a substrate for an ink jet recording head, incorporating functional elements for driving the head.
Also, Japanese Patent Application Laid-Open No. 3-5151 discloses that in a substrate for an ink jet recording head, a bubble-generating heater and an ink-preheating heater are formed in the same layer by using the same material, and that heating of the substrate for the head by such preheating heater prevents the deterioration of the discharge characteristics at a low-temperature situation.
In relation to the heating method by such preheating heater, a method for controlling ink viscosity according to gradation signals is disclosed in Japanese Patent Application Laid-Open No. 3-146349, and a method for maintaining a recording head at a constant temperature during recording operation is disclosed in Japanese Patent Application Laid-Open No. 3-43254.
FIG. 9 shows a configuration of a conventional substrate for an ink jet recording head, comprising a preheating heater.
As shown in FIG. 9, this conventional example is composed of a bubble-generating heater 9003 formed by a heat-generating resistance member (not shown) for generating heat required for bubble generation in the ink, wirings 9004 for supplying an electrical current from a power supply (not shown) to the heat-generating resistance member, and a preheating heater 9005 formed by a heat-generating resistance member for generating additional heat to be applied to the recording head portion.
In general, the substrate for the ink jet recording head is formed by repetition of the steps of carrying out film formation of a resistance member, a wiring metal and an insulating film, for example, on a silicon substrate and then executing patterning by photolithography. Also, in case of forming functional elements such as integrated circuits at the same time on the same base member, there is repeatedly executed the steps commonly employed in the semiconductor device manufacture.
In such operation, in order to reduce the production cost by increasing the number of the substrates for the ink jet recording head per one starting silicon substrate, it is required to reduce, as far as possible, the size of the substrate for the ink jet recording head. For this purpose, it is required to reduce the size of the bubble-generating heater and of the functional elements such as integrated circuits, and to improve the efficiency of arrangement of the wirings.
However, such conventional substrate for the ink jet recording head has the following problems, because the bubble-generating heater and the preheating heater are formed in the same plane.
(1) In case a higher level of integration is intended by arranging a plurality of the bubblegenerating heaters, the preheating heaters cannot be positioned close to the bubble-generating heaters because power-supplying wirings are present in the vicinity of the bubble-generating heaters. As the result, the substrate becomes inevitably large.
(2) At a low temperature condition, the amount of heat for preheating has to be increased. In such case, there is required a relatively large preheating heater in order not to achieve the preheating without bubble generation. As the result, the substrate becomes inevitably large.
(3) In case the bubble-generating heaters are arranged at a high level of integration as in the above (1), the preheating heaters cannot be positioned behind such bubble-generating heaters or in the area of the integrated circuits, but have to be positioned only at the side of thus arrayed bubble-generating heaters. As the result, the substrate becomes large in size in the direction of array of the bubble-generating heaters.